In some interventional X-Ray procedures it is common to inject an embolization agent into the patient to effect various treatments for instance, AVMs (Arteriovenous Malformations) or tumors. For example, in order to stem growth of cancerous tissue or of an AVM (arteriovenous malformation) its arterial feeders may be intentionally embolized to shut down the blood supply (AVM) and/or stop nutrient supply to the cancer or growth (such as in transcatheter arterial chemoembolization (TACE)). This type of intervention, called medical embolization, may be brought about by administering an embolization agent at a desired location (region of interest (ROI)) in the human body by way of a catheter tube. The embolization agent is essentially a liquid volume or mass of glue comprising small beads suspended in a carrier liquid through which the occlusion at the diseased location effected. During such embolization interventions it is pre-eminent to ensure that it is only the targeted arterial feeders that are blocked off but sound vessels are not. At present the position of emboli is monitored by acquiring one or more fluoroscopic projection images. Because of radiation opacity of the embolus and/or of the carrier fluid, projective “footprints” are discernible in said fluoroscopic images thereby providing clues to an interventionist radiological about the embolus' whereabouts.
The embolization agents are usually poorly visible under X-ray fluoroscopy. To help better visualize the deposition of embolization agent, subtraction techniques are regularly used which eliminate the background and leave only the deposited embolization agent. However, using existing subtraction techniques in this context have proved in the past remarkably cumbersome and fiddly. In particular, they have relied on selection of mask images, requiring a frame (“mask”) selection every few fluoroscopy runs. The resulting subtraction image shows generally only a tiny black smear of deposited embolization agent, which is very hard to distinguish from subtraction artefacts and background noise.
Another issue with embolization procedures is that in most trans-arterial embolization (TAE) procedures it is important to estimate the amount of deposited material in the target tissue. The estimate might be used to predict the clinical outcome or it might be used to check if part of the injected material was deposited elsewhere. However, to achieve these estimates, the use of expensive additional equipment is usually necessary.